1. Field of the Invention
The present invention relates to a method for fabricating LED modules and more particularly, to such a LED module fabrication method, which employs an over molding technique to primarily mold a packing cup on a circuit substrate around a LED chip and then to secondarily mold a lens on the LED chip and the packing cup, so that no any gap is left in the lens, avoiding deflection, total reflection or light attenuation.
2. Description of the Related Art
Many different lighting fixtures using different light-emitting techniques are commercially available. Nowadays, LED (light emitting diode) has been intensively used in embedded lamps, head lamps and many other different lighting fixtures for the advantages of excellent photoelectric conversion efficiency, constant wavelength, adjustability of luminous flux and light quality, small size, low heat value and long lifespan.
Following fast development of LED material and packaging technologies, high performance and high brightness LED modules have been intensively used in signboards, vehicle head lamps and outdoor lightings to substitute for conventional lamp bulbs or lamp tubes. Conventional LED modules usually adopt chip-on-board packaging. Chip-on-board packaging is a semiconductor assembly technology where the LED chip or die is directly mounted on the circuit board. This packaging technology is a small-sized surface mount technology. The chip or die is electrically connected to the contacts at the circuit board or circuit substrate by wire bonding. After wire bonding, an encapsulation technique is employed to cover the bonding wires and the chip or die with a resin.
FIG. 9 illustrates a conventional chip-on-board LED module. According to this packaging method, a LED chip A is mounted on a heat sink B1 in an insulation layer B, and then conducting wires A1 are respectively bonded to the LED chip A and positive and negative metal terminals C;D that extend through the insulation layer B, and then a packaging resin E is packaged on the LED chip A, and then a lens F is bonded to the resin E. This design of chip-on-board LED module has drawbacks as follows:
1. The packaging resin E is adapted for protecting the LED chip A and allowing transfer of waste heat from the LED chip A to the outside. However, when the light emitted by the LED chip A passes through the packaging resin E into the lens F, it is refracted at the first time. When the light passes out of the lens F, it is refracted at the second time. In order to eliminate aging of the packaging resin E, a glass lens used and directly bonded to the LED chip A. However, directly bonding a glass lens to the LED chip A cannot eliminate the problem of existence of a gap in between the glass lens and the LED chip A. The presence of gaseous media in between the glass lens and the LED chip A will cause deflection, total reflection or light attenuation.
2. When soldering the LED chip A to the circuit substrate by surface mount technology, it is performed at a high temperature about 250° C. to 300° C. During this stage, the packaging resin E is heated to cause aging, and the lens F is heated to contract. Aging of the packaging resin E affects the performance of surface mount technology. Contracting of the lens F causes a curvature change, affecting the entire optical quality and lowering the luminous brightness and uneven distribution of light.
Therefore, it is desirable to provide a LED module packaging method, which eliminates the aforesaid problems.